A photon transmission method was used to probe the evolution of transparency during film formation from poly(methyl methacrylate) (PMMA) particles with different molecular weight. The latex films were prepared from low (LM) and high (HM) molecular weighted PMMA particles at room temperature and annealed at elevated temperatures in various time intervals above glass transition (T-g). It was observed that transmitted photon intensities (I-tr) from these films increased as the annealing temperature was increased. It is seen from I-tr curves that there are two distinct film formation stages, which are named as void closure and interdiffusion processes, respectively. The activation energies for viscous Row and backbone motion were obtained using well-defined models. Viscous flow activation energies (DeltaH) were found to be around 150 and 134 kJ/mol for LM and HM films, respectively. Backbone activation energies (DeltaE(b)) were found to increase from 142 to 199 and 59 to 98 kJ/mol in time of annealing for LM and HM films, respectively. Healing points (tau (H),T-H) were determined and using these time-temperature pairs, healing activation energies (DeltaE(H)) were measured and found to be 188 and 117 kJ/mol for LM and HM films, respectively. (C) 2001 Elsevier Science Ltd. All rights reserved.